It could be a magazine issue and not the slide release. I'd try a different magazine before doing anything else. The extended mag may not be seating properly because of that sleeve at the base too. Try inserting the magazines one by one without the slide on. Pay attention to how much the slide stop moves with each magazine.

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Regret for the things we did can be tempered by time; it is regret for the things we did not do that is inconsolable."
-Sydney J. Harris